Dependence to the narcotic drugs has long posed a problem because of both the biological and sociological implications. The increasing research effort into the biochemical, physiological and pharmacological actions of the narcotics promises to greatly expand our rather limited knowledge of the anatomical and physiological pathways involved. Continued use of opiates, whether as the result of abuse or treatment of intractable pain, may lead to drug dependence (addiction). It has been demonstrated that thalamic lesions, specifically in areas of pain perception, can modify the effects of withdrawal in humans and rats addicted to the narcotics. It is the purpose of this study to continue an investigation into the effects of lesions in various brain areas, particularly thalamic and limbic, on dependence to the narcotic drugs. Effects of the lesions on production of dependence and the severity of the abstinence syndrome will be observed. Of particular interest is the importance of chronicity of lesions and factors such as differential housing.